Rapid bone loss is associated with increased levels of biochemical markers

We examined associations of biochemical markers of bone turnover with rapid bone loss, as measured by changes in bone mineral density (BMD). To improve the precision of bone loss estimates, calcaneal BMD was measured up to eight times over a long interval (13 years) among postmenopausal women (mean age = 62 years at baseline). Women with fractures during the previous year, and users of corticosteroids, active vitamin D, bisphosphonates or calcitonin were excluded to avoid potential transient effects on marker levels. Among the remaining 354 women, markers were measured for 100 women with the fastest BMD loss (rapid loss group; mean = 2.2%/year) and 100 with the slowest loss (mean = 0.4%/year). Two markers of bone formation, serum bone alkaline phosphatase (Alkphase-B; BAP) and osteocalcin (NovoCalcin; OC), and two markers of bone resorption, urinary creatinine-corrected free deoxypyridinoline (Pyrilinks-D; DPD) and free pyridinolines (Pyrilinks; PYD), were measured. In separate logistic regression models, each of the markers was strongly associated with rapid loss: the odds of rapid loss increased by 1.8 to 2.0 times for each 1.0 standard deviation (SD) increase of the marker. For BAP levels 2 SD above the mean, the probability of rapid bone loss was 80%; in contrast, the probability was only 20% at 2 SD below the mean. The other markers yielded similar results. We conclude that these markers are associated with rapid bone loss; this relationship appears to be continuous, with progressively greater risk of rapid bone loss with increasing levels of biomarkers. Prospective studies that include the entire distribution of bone loss rates are warranted to confirm these findings.